Dynamic quantum decoherence in Stern-Gerlach experiment

The Stem-Gerlach (SG) experiments considered as a quantum measurement proce ss measuring the spin states of particles from their spatial distribution. The wave packet collapse or quantum decoherence can he described as a dynam ical evolution governed by the interaction between the space degrees of fre edom and the spin degrees of freedom. The analytic solution of this exactly solvable model shows that the decaying process of coherence with time in t he SG experiment obeys no longer the linear exponential law.